|How to Use IS & ASET|
|Taking IS Photos|
|Using ASET Scope|
|Reference Chart - IS|
|Reference Chart - ASET|
|Light Return & Shadow|
|Fancy Shapes - IS & ASET|
|HCA CUT CALCULATOR(free)|
FANCY SHAPED DIAMONDS
The ideal-scope principle also works with fancy shaped diamonds but ASET is better for fancy shapes.
Fancy shaped diamonds (all shapes other than round) do not return light as well as ideal cut rounds. The ideal-scope goal of plenty of red, a small amount of evenly distributed darkness and little or no white leakage is difficult, if not impossible to achieve. Evenly distributed small areas of means a diamond will not have large dead zones.
If much of the diamond is red or pink, it will naturally be brighter and likely more brilliant.
Fancy cuts (other than step cuts like Emerald cuts) often appear to have a lot more very small facets. If many of these virtual facets show partial light return through the ideal-scope then the stone is likely to display lots of tiny flashes of fire.
Princess and Radiant
Square cuts have the potential for better light return than rectangular stones; the longer the length to width ratio, the more variation in pavilion angles. This means a stone will be steeper across the short direction and shallower across the length of the stone.
This stone leaks more in the left and right sides because the pavilion angles across the short direction are too steep, where-as lengthwise the stone has a better shallower pavilion.
This set is arranged from best to worst light return. The dark spots are a good sign; if they are small and well dispersed the diamond is likely to show more fire. The best and the worst of these 4 stones are shown below in DiamCalc images so we can compare their light return and fire. Note that the diamond with a better Ideal-Scope image has brighter realistic photos through rotation of 30° in 3x10° steps.
Princess cuts often have better light return near the centre, but generally leak more near the edges or corners. Try to avoid stones with large triangular shaped windows like the stone below.
Leakage windows like this are common in princess and some other fancy cuts. Stones like this will have dull patches with little light return or fire from those regions.
Emerald Cuts often show a cross-shaped pattern in pink with a lot of leakage in the small corner facets. If the pavilion facets on the ends are cut too deeply emerald cuts can show see-through triangular windows; like princess cuts. The best performing emerald cuts have some black and a lot of red to pink evenly balanced around the diamond.
The ideal keel length (the long line or culet on the bottom) is:
Length - Width = Keel length
This ensures that side and end pavilion angles are the same. These five stones represent very good to fair stones.
Pear shapes, Ovals & Marquise
Bow Tie Region
often cut from very shallow rough,
vary a lot in proportions, and therefore
in visual performance. Very good
light return in a trilliants is
rare; a pleasing shape should be
a key concern.